This invention relates to terrain visualization as it would appear from a vehicle moving above the earth's surface, the visualization being accomplished by ray tracing a known height field that has been transformed into an array of cones of empty space balanced on points near the terrain and opening upwards while avoiding interception with other vertical protuberances in the earth's surface, thereby to facilitate determination of points where rays through pixels in perspective view displays first pierce terrain at a substantial reduction in computational steps.
Terrain visualization finds much use for simulation of aircraft flight, and for providing a preview of terrain which may be unfamiliar to the pilot. Such visualization has been accomplished by a variety of methods which include the step of generating height data corresponding to each pixel of a perspective view display by a ray tracing technique employing a preexistent map of the earth's surface. The map is a height field containing the height of each point on a grid of the earth's surface. Such height fields may be expressed in terms of volume elements, or voxels, wherein, for example, the rectangular volume elements may differ in height but have bases at height zero.
In the case of a view of terrain from an aircraft flying at altitudes that do not greatly exceed the altitude of objects on the earth's surface, such as tall buildings and hills, such a view which is inclined only slightly relative to the horizon may experience significant blockage of the surface features of the earth by buildings and hills. This blockage adds complexity to the ray tracing procedure because it is necessary to insure that one obtains the intercept of the ray with the obstruction such as the building or the hill, rather than obtaining an erroneous reading of data of terrain blocked from view by tracing the ray to a portion of the earth's surface for which the view is blocked by the obstruction. To ensure accuracy, ray tracing is normally conducted by incrementally stepping along the ray, one voxel at a time, to check for the presence of an obstruction.
A problem arises in that the foregoing ray tracing procedure is unduly time consuming for situations in which terrain visualization displays are to be updated rapidly, as in the case of simulating a rapidly moving aircraft. For example, real time visualization is precluded with available ray tracing procedures. As a result, the utility of ray tracing for terrain visualization is severely restricted.